GCN Circular 10659
David Gruber (MPE) reports on behalf of the Fermi GBM Team: "At 05:51:25.75 UT on 23 April 2010, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 100423B (trigger 293694687 / 100423244). The on-ground calculated location, using the GBM trigger data, is RA = 119.7, DEC = 5.8 (J2000 degrees, equivalent to 07h 58m, 05d 46'), with an uncertainty of 1.5 degrees (radius, 1-sigma containment, statistical only; there is additionally a systematic error which is currently estimated to be 2 to 3 degrees). The angle from the Fermi LAT boresight is 40 degrees. The GBM light curve consists of one pulse with a duration (T90) of about 21.6 +/- 1.1 s (8-1000 keV). The time-averaged spectrum from T0-2.0 s to T0+23.6s is best fit by a power law function with an exponential high energy cutoff. The power law index is -0.84 +/-0.05 and the cutoff energy, parameterized as Epeak, is 1034 (+144/-117) keV (CSTAT 1395.6 for 845 d.o.f.). The event fluence (8-1000 keV) in this time interval is (1.226 +/- 0.019)E-5 erg/cm^2. The 1.024-sec peak photon flux measured starting from T0+5.3 s in the 8-1000 keV band is 3.53 +/- 0.13 ph/s/cm^2. A Band function fits the spectrum equally well (CSTAT 1394.3 for 844 d.o.f.) with Epeak= 1006 (+122/-113) keV, alpha = -0.83 (+0.05/-0.04) and beta = -3.15 (+0.45/-1.24). The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog."